1990 MX5 (NA) will not start when cold but runs after bump start

Technical Area Engine, Transmission, Exhaust etc
2

Hi all,

Sorry to make this my first post, I have recently aquired a 1990 MX5 in red.  The car has been fantastic up untill last night.

Problem:

The car cranks, makes the occasional splutter but will not start.  If I tow the car up to about 10-15 mph, and bump start it, it runs normally performing as expected.  Once I had the car running and at operating temperature, I shorted pin10 to ground, and set the idle speed, as I was not sure if this could give it a hard time starting.  Once the car had cooled down again this evening, I get the same problem, car turns over but will not start.  I can’t hear the fuel pump priming when I switch the car to the ignition position, but if I short the FP pin to ground, it does come on with the ignition, but this does not allow me to start the car.  The battery will eventually flatten if I continue trying to start it. 

Other points of note, upon trying to use “cold start” once yesterday, and it produced a significant backfire (I do not mean afterfire, as in the fuel igniting in the exhaust system, I mean, explosion in the intake section).  The battery has been enough to start the car ok up untill now, but it does not seem to turn the engine over especially energetically, but I do not know if this is normal for the car.  It has also been much colder these last couple of days.  My throttle cable is set quite taught, but I didn’t think this would create much of a problem, as it usually requires about 10% throttle to go anyway.  The spark plugs and leads look to be in recently replaced condition.

Thanks very much for any assistance!

977

3

The first signs of a battery about to fail. Three or four choices

Get hold of a trickle charger, similar to the C Tek…google and see if you can rejuvenate your battery.

Buy a new battery from MX5 parts.

My choice, buy a new battery from Mazda, the most expensive in therms of outlay, but it will last 3 times as long and is a straight swop.

Last may be an alternator problem put a meter set to volts across the terminals of the battery, fully charged it should read 14.3 ish volts

Good luck--------

4

I tried using another car with leads, and it still won’t go, even though it is a 70AH battery in a 2.5L bmw.

I would guess the car is running very rich/flooded? The plugs are wet when I take them out having tried to start it.

Any other ideas ?

Thanks,

David

5

Today, I bumped the car, started first time, drove it down to Halfords (god forsaken dumpster of a store that ought not dare affiliate itself with motorsport), picked up a new set of plugs (ÂŁ12, not as ripped off as expected), got back, stuck em in.

I waited until just now (22:36) which should have given it time to cool right down. The car (I typed “she” initially… oh dear!) started after a couple of seconds on the key.

I’m working away tomorrow night, but the evening after I’ll try her again, if it goes again I would imagine the new plugs have done enough of the trick. :slight_smile:

If not I guess next up is to get a set of leads in there - what are best value and from whom should I purchase them?

6

Update:

After a new set of plugs, carefully seated plug wires, she just started on the button, first go at -3 degrees C.

Shrug =)

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